Q-angle abnormality is one of the clinical symptoms of patellar instability, and patellar instability (unstable patella) is a common cause of anterior knee pain, a common disease of the patellofemoral joint, and an important cause of chondromalacia or osteoarthritis of the patellofemoral joint. Advances in biomechanics and imaging technology, as well as the diversification of clinical testing methods, have led to the recognition that degenerative changes in the patellofemoral joint are mostly due to patellar instability caused by poor patellofemoral joint fit or patellar force line malalignment, such as patellar deviation, patellar tilt, patellar elevation, patellar subluxation, etc. The causes of patellofemoral instability, patellar deviation or subluxation actually include abnormalities of every structure in the anterior knee area, which are summarized into the following four categories: 1. abnormalities of the quadriceps muscle and its expansion section including atrophy or dysplasia of the medial femoral muscle, relaxation and rupture of the medial supporting ligament or tearing of the lateral supporting ligament tension and high patella. 2, knee joint force line abnormalities including increased Q angle, as well as knee valgus and knee retroflexion. 3, abnormal patella shape such as split patella (patella bipartite), heterogeneous patella (type III, IV). 4, congenital factors Mainly refers to dysplasia of the femoral condyle secondary to deformation or abnormal shape of the femoral epicondyle, etc. The common feature of all these changes is that the patellofemoral joint loses its normal structure, resulting in abnormal tensile stress acting on the patella or abnormal patellar motion trajectory, leaving the patella in an unstable state.